1. Field of the Invention
This invention relates to plating or etching of metals onto or from a substrate with or without laser enhancement and more particularly to employment of masking techniques to enhance the process of plating, or etching.
2. Description of the Prior Art
Electroplating:
In electroplating, an anode and a cathode are placed in an electrolyte and an external voltage is applied from a power supply to produce a plating current. The current flow causes cations (metal ions) to be transported to the cathode where they are deposited.
U.S. Pat. No. 4,217,183 of Melcher et al for "Method for Locally Enhancing Electroplating Rates" describes maskless electroplating with the enhancement provided by using an electromagnetic beam such as a laser beam to increase the plating rate preferentially in a selected area up to 1,000 times the rate which would have been achieved in the absence of the laser beam. The increased rate of plating occurs while the laser beam is directed upon the areas of a substrate to be plated and the beam is scanned with a rotating mirror. The process is a sequential process. The beam has a power in the range from 100 w/cm.sup.2 to 1,000,000 w/cm.sup.2 at the focal spot where plating is occurring.
U.S. Pat. No. 3,898,417 of Atkinson for "Continuous Strip Encoding" describes laser coating of a continuous strip of metal sheet. The coding can be applied to the sheet before or after plating. The coding provides indices which can be read subsequently and has nothing to do with the plating process itself. An array of laser elements for forming coding marks is shown. The patent does not relate to masking.
Masking:
U.S. Pat. No. 3,956,077 of Hamby et al "Methods of Providing Contact Between Two Members Normally Separable by an Intervening Member" shows a polymer substrate clad with a copper coating with a dry photopolymer mask. Copper is plated onto portions of copper exposed through the mask, to form printed circuits.
U.S. Pat. No. 3,632,205 of Marcy "Electrooptical Image-Tracing System Particularly for Use with Laser Beams" describes computer control of laser scanning. It mentions thick photoresist and "a substrate which is to be exposed, etched or the like, particularly when microcircuits are to be produced . . . . " The laser beam is driven by means of digital positioning, preferably under computer control. "With a low power laser, masks are produced from photosensitive plates which are exposed to the source. Using a more powerful laser, for example an argon laser, layers of a photoresist, successively deposited on the substrate are directly exposed. Using a very high power laser . . . a mask can be produced using the laser energy to cut a metal plate".
U.S. Pat. No. 4,262,186 of Provancher "Laser Chem-Milling Method, Apparatus and Structure Resulting Therefrom" teaches the provision of a masking template with a hole pattern which is placed over a masked surface of a material to be milled chemically. The mask is then perforated by a laser beam shining through holes in the template. The laser beam remains at each hole for enough time to burn the maskant from the surface of the substrate to be chemically milled. While openings of patterns in a mask are taught by Provancher, it is not taught that one can open a mask by means of independently scanning a laser beam under automatic control or without the use of an intervening template, and it does not teach plating with laser enhancement.
Electroless Plating:
In electroless deposition, a local charge transfer occurs by a discharge of ions at the workpiece-electrolyte interface which is activated by decomposition of a reducing agent at the catalytic surface solution interface. None of the substrate material, onto which the plating occurs, is dissolved.
U.S. Pat. No. 4,239,789 of Blum et al for "Maskless Method for Electroless Plating Patterns" describes a selective plating process for the surfaces of a workpiece in which the workpiece is contacted with a plating solution. During plating, regions to be plated are selectively subjected to a focussed electromagnetic beam which results, at the selected regions, in local heating and an increased plating rate.
Exchange Plating:
In typical exchange plating processes, a surface of a less noble metal is immersed in a solution of a more noble element. The typical metal surface is covered with many cathodic and many anodic regions on a microscopic scale in the form of crystallites and intergranular regions. Because of difference in the electrochemical potential between the grains and the intergranular regions, local electrochemical cells are set up in which the less noble element leaves the electrons behind at the anodic regions and goes into solution in a form of ions. The more noble element ions present in the solution deposit at the cathodic regions where they acquire the electrons released during the dissolution of the less noble metal element. One can deposit Cu onto Ni, Au onto Ni, Au onto Cu and Pd onto Cu. Where the substrate is an insulator carrying a thin film of a metal, dissolution of the less noble metal adjacent to an area to be plated isolates the plated regions electrically.
Kulynych et al "Laser-Enhanced Exchange Plating" IBM Technical Disclosure Bulletin Vol. 23 No. 3, 1262 (August 1980) describes a laser enhanced plating process.
U.S. patent application Ser. No. 287,661, filed July 28, 1981 now U.S. Pat. No. 4,349,583, of Kulynych et al "Laser Enhanced Maskless Method for Plating and Simultaneous Plating and Etching of Patterns" describes a method for high resolution maskless plating with an immersion, exchange or like plating bath. Preferential plating results from exposing those regions where plating is to be performed to an energy beam to increase the plating rate and the resulting highly localized plating thickness is several orders of magnitude greater than is possible by standard immersion techniques.
Maskless Chemical and Electrochemical Machining:
U.S. Pat. No. 4,283,259 of Melcher et al for "Method for Maskless Chemical and Electrochemical Machining" describes a method for high resolution maskless chemical and electrochemical machining. Preferential etching results from exposing those regions where machining is sought to an energy beam. Such exposures can increase the etching rate in the case of electrochemical machining by a factor of 1,000 to 10,000. Such enhancement is sufficient to make masking unnecessary.